Spectrophotometric sampling cells



' March 3,1970 I J. TADAYON SPECTROPHOTOMETRIC SAMPLING CELLS Filed Dec. 3, 1964 INvau-roe JZIMHL 7710A YON ATTORNEV5.

United States Patent 3,498,068 SPECTROPHOTOMETRIC SAMPLING CELLS Jamal Tadayon, Richmond, Surrey, England, assignor, by

mesne assignments, to Beckman Instruments, Inc., Fullerton, Calif. I

Filed Dec. 3, 1964, Ser. No. 415,601 Claims priority, application Great Britain, Dec. 10, 1963, 48,797/63 Int. Cl. G0ln 21/16; F25j 1/02 US. Cl. 6240 14 Claims ABSTRACT OF THE DISCLOSURE A sampling cell formed from a tube of suitable material to provide an inlet conduit and a cell chamber adapted to hold a sample for spectrometric examination, the cell chamber having parallel walls with fused edges and encased in a rigid container, some forms of the cell having an inlet chamber and condensing apparatus for introducing the sample into the cell, the apparatus including an inlet nozzle assembly and refrigerant in a container.

This invention relates to spectrophotometric sampling cells, especially sampling cells for use in the infra-red region of the spectrum.

The invention provides a spectrophotometric sampling cell formed from a tube of spectrophotometrically acceptable material, that is, material which is chemically inert to the spectrometric specimen and optically transparent to the radiation of the spectrometer in the region of interest, and wherein a portion of the tube forms an inlet conduit and an adjacent portion of the tube is flattened to form a cell chamber that is in communication with the inlet conduit, the cell chamber having two substantially parallel plane walls and the opposing portions of the flattened tube being fused together beyond the lateral edges of the cell chamber.

There may be provided a second conduit communicating with the cell chamber and situated at the end of the cell chamber remote from the inlet conduit, the second conduit being formed from a further portion of the tube. Air can escape from the cell chamber through the second conduit when the cell is filled through the inlet conduit. When the sampling cell is provided with an inlet conduit only, the opposing end portions of the flattened tube remote from the inlet conduit are fused together in order to close the end of the cell chamber.

There may also be provided an inlet chamber having and internal cross-sectional area greater than the internal cross-sectional area of the inlet conduit and communicating with the end of the inlet conduit remote from the cell chamber. The inlet chamber may be formed from a further portion of the tube, so that it is integral with the inlet conduit and constructed of a spectrophotometrically acceptable material. When the inlet chamber forms an integral part of the sampling cell, the shape of the cross-section of the inlet chamber should be such that a closure member for the inlet conduit may be passed through the inlet chamber. Advantageously, the inlet chamber is non-integral with and separable from the inlet conduit, and is in the form of a generally tubular vessel, one end portion of the vessel being in the form of an outlet conduit capable of being inserted into the open end of the said inlet conduit of the sampling cell.

The inlet chamber serves as a chamber in which a gaseous sample from a gas chromatography apparatus may be condensed when the inlet chamber is cooled. The cooling may be effected by placing the inlet chamber in a bath containing, for example, liquid oxygen, air or nitrogen, or solid carbon dioxide. When the inlet chamber is an integral part of the sampling cell, it is, of course, necessary to place both the cell chamber and the inlet chamber in the refrigerant, but when the inlet chamber is non-integral with and separable from the inlet conduit of the sampling cell, the inlet chamber may be separated from the remainder of the sampling cell and a sample may be condensed in the inlet chamber alone, provided that a suitable closure is provided for the outlet conduit. The sample may be retained in the separate inlet chamber for storage by providing a suitable closure for the entrance to the inlet chamber.

The sample may be transferred from the inlet chamber to the cell chamber by centrifuging. In order to prevent the loss of a volatile sample from the sampling cell by vapourisation, a well-fitting gung is fitted into the inlet conduit as soon as the sample has been transferred to the cell chamber. It is convenient for the inlet conduit to have a circular cross-section. Preferably, the walls of the inlet conduit taper towards the cell chamber so that the bung can be pressed tightly into the inlet conduit.

The spectrophotometrically acceptable material may be silver chloride or polyethylene, which are both spectrophotometrically acceptable materials for the infra-red region of the spectrum, which may be readily formed into the shapes required and which are capable of being fused under the action of heat and pressure. When the inlet chamber is non-integral with and separable from the inlet conduit of the sampling cell it is preferably manufactured from glass, a material that is robust and easily cleaned and which does not deteriorate when stored.

The thickness of the cell chamber formed in the flattened portion of the tube is preferably within the range of from 10 microns to 1 mm..

The present invention also provides a process for the manufacture of a spectrophotometric sampling cell, which comprises placing a spacer having the thickness of the cell chamber within a tube of spectrophotometrically acceptable material, the spacer extending beyond at least one end of the tube, applying heat and pressure to a part of the tube containing the spacer in order to flatten that part and fuse together opposing portions of the flattened tube beyond the lateral edges of the spacer, so that a cell chamber having two substantially parallel plane Walls is formed containing the spacer, and withdrawing the spacer from within the tube, a portion of the tube adjacent to the flattened part forming an inlet conduit communicating with the cell chamber.

When the sampling cell is not provided with a second conduit as hereinbefore described, the opposing end portions of the flattened tube remote from the inlet conduit are also fused together in order to close the end of the cell chamber. The opposing end portions may be fused together before or after the spacer is withdrawn from within the tube.

A sampling cell provided with an integral inlet chamber may be formed from a tube having two portions, the internal cross-sectional area of the first portion being greater than the internal cross-sectional area of the second portion, the sampling cell being formed from. the second portion of the tube and the first portion forming the inlet chamber.

The tube from which the sampling cell is manufactured may be moulded from a spectrophotometrically acceptable material in an impression moulding machine. When the sampling cell is provided with an integral inlet chamber the tube having two portions of different internal cross-sectional area may be formed by drawing a portion of a tube having a uniform cross-section through a die in order to increase the internal cross-sectional area of that portion.

Advantageously, the sampling cells of the present invention are mounted in a rigid container in order that they may be more robust and more conveniently handled in use. The rigid container is provided with windows having a size, shape and position such that radiation may pass through the cell chamber of the sampling cell. The rigid container is advantageously manufactured from a rigid inert plastic material such as, for example, a phenolformaldehyde resin.

In order that a gaseous sample entrained in a carrier gas may be introduced into a spectrophotometric sampling cell without condensation of the sample before it reaches the sampling cell, the present invention also provides an inlet nozzle assembly, which comprises an inner tube' constructed of metal for the passage of the mixture of carrier gas and gaseous sample, an outer tube constructed of metal surrounding the inner tube and being attached to and in electrical contact With the inner tube at the outlet end thereof, and an electrically insulating member positioned between the inlet end of the inner tube and the outer tube, the outer tube being provided with two orifices so that, in operation, a gas can enter the space between the inner and outer tubes through one orifice and leave that space through the other orifice, and the arrangement of the inner and outer tubes being such that, in operation, an electric heating current can flow through the inner and outer tubes. The gaseous sample entrained in a carrier gas may have been obtained from a gas chromatography apparatus.

In accordance with the present invention, several forms of sampling cells, two of them provided with an inlet chamber, processes for the manufacture of sampling cells and an arrangement for condensing a sample from a gas chromatography apparatus in a sampling cell will now be described in greater detail by way of example with reference to the accompanying drawings, in which:

FIG. 1 is an axial section through a tube of spectrophotometrically acceptable material from which a sampling cell is manufactured, and which also contains a spacer.

FIG. 2 is a plan view of one form of sampling cell.

FIG. 3 is a side elevation of the form of sampling cell shown in FIG. 2.

FIG. 4 is a plan view of a second form of sampling cell.

FIG. 5 is an axial section through one form of sampling cell provided with an inlet chamber, the sampling cell containing a closure member for the cell chamber.

FIG. 6 is an axial section through a second form of sampling cell provided with an inlet chamber.

FIG. 7 is an axial section through an arrangement permitting a gaseous sample from a gas chromatography apparatus to be condensed in a sampling cell.

Referring to FIG. 1 of the drawings, a tube 1 of spectrophotometrically acceptable material, for example, silver chloride, is formed in an impression moulding machine from a block of the material. The tube 1 has a circular cross-section thrgughout and may have a wall thickness at a u 2 mm, The en po t on 2 of h tub l is tapered outwardly towards the end of the tube. A spacer 3 having the thickness of the cell chamber is positioned within the tube 1, the spacer extending beyond the endof the tube adjacent to the end portion 2.

In a process for the manufacture of a sampling cell from the tube 1 containing the spacer 3, heat and pressure were applied to the cylindrical part of the tube containing the spacer in order to flatten that part and fuse together opposing portions of the flattened tube beyond the lateral edges of the spacer. Referring to FIGS. 2 and 3 of the drawings, a cell chamber 4 having two substantially parallel plane walls is thus formed containing the spacer 3. The portions of the flattened tube that were fused together are indicated by the reference numeral 5, and the application of heat and pressure also fused together opposing end portions of the flattened tube remote from the end portion 2 in order to close the end of the cell chamber 4.

After the formation of the cell chamber 4 the spacer 3 was Withdrawn from within the tube 1. The end portion 2 of the tube 1 forms an inlet conduit for the cell chamber 4, and the shape of the end portion is such that a well-fitting bung of substantially frusto-conical shape can be pressed tightly into the inlet conduit.

Referring to FIG. 4 of the drawings, the second form of sampling cell is formed from a tube of spectrophotometrically acceptable material, for example, silver chloride, and has an inlet conduit 6, a cell chamber 7 situated in a flattened portion of the tube, and a second conduit 8 communicating with the cell chamber and situated at the end of the cell chamber remote from the inlet conduit. The inlet conduit 6 and the cell chamber 7 have the same shape as the corresponding parts of the sampling cell shown in FIGS. 2 and 3, and the second conduit 8 has the same shape as the inlet conduit 6.

The process for the formation of the cell chamber 7 in a tube of spectrophotometrically acceptable material is similar to the process described hereinbefore with reference to FIGS. 1 to 3, except that the action of heat and pressure does not close the end of the cell chamber remote from the inlet conduit 6.

Referring to FIG. 5 of the drawings, a sampling cell of the form shown in FIGS. 2 and 3 having an inlet conduit 9 and a cell chamber 10 is provided with an integral inlet chamber 11. The inlet chamber 11 has a circular internal cross-sectional area greater than the internal crosssectional area of the inlet conduit 9. The sampling cell is formed from a tube having two portions, the first portion being of larger internal cross-sectional area than the second portion. The cell chamber 10 is formed within the second portion by a process similar to that described hereinbefore with reference to FIGS. 1 to 3. The part of the second portion adjacent to the first portion of the tube is not flattened, and forms the inlet conduit 9. A closure member 12 is shown in FIG. 5 positioned so as to close the inlet conduit 9, the closure member having a handle 13 for inserting the closure member into the inlet conduit.

Referring to FIG. 6 of the drawings, a sampling cell of the form shown in FIGS. 2 and 3 having an inlet conduit 14 is provided with an inlet chamber 15 non-integral with and separable from the remainder of the sampling cell. The inlet chamber 15 is provided with an outlet conduit 16 so shaped that it may be inserted into the inlet conduit 14. A resilient sleeve piece 17 that fits inside the end of the inlet conduit 14 of the sampling cell is placed around the end of outlet conduit 16 in order to prevent any loss of the sample from between the inlet conduit 14 and the outlet conduit 16. The sleeve piece 17 may be dispensed with if the outlet conduit 16 is so shaped that it fits tightly into the end of the inlet conduit 14. The inlet chamber 15 is preferably constructed of glass.

It will be appreciated that the cell chamber of each of the sampling cells formed as hereinbefore described is a fragile item which requires very careful handling. There: fore, anything that will render them more robust and add to the convenience of handling, without interfering with the spectrometric examination, is desirable. Although the fused opposing portions 5 are helpful to this end, it is preferred also to provide a protective jacket or container 37 having an open area or window 38 on each side, the container encasing portions of the cell chamber and being of a suitable material having substantial rigidity, for example, an inert plastic resin. As seen in FIGS. 2-4, the jacket or container 37 is utilized to rigidify the opposing portions 5. It is understood, of course, that additional portions could be similarly encased, for example, the walls of the cell chamber, in which case the openings or windows would be smaller in size and could be of a material suitable for the transmission of the spectrometric radiation.

Referring to FIG. 7 of the drawings, the arrangement for permitting a gaseous sample from a gas chromatography apparatus to be condensed in a sampling cell comprises a Dewar flask 18 containing a liquid refrigerant 19, a sampling cell 20 provided with an integral inlet chamber 21 (the sampling cell being of the form shown in FIG. 5), an inlet nozzle assemby indicated generally by the reference numeral 22, and an inlet pipe 23 in communication with the outlet of the gas chromatography apparatus.

The inlet nozzle assembly 22 comprises an inner tube 24 surrounded by a coaxial outer tube 25. One end of the tube 24 is provided with a recess 26 into which the end of the inlet pipe 23 can be inserted. The outer end 27 of the tube 24 projects into the interior of the inlet chamber 21 when the inlet nozzle assembly 22 is in the operative position. The end of the outer tube 25 close to the end 27 of the tube 24 is attached to and in electrical contact with the tube 24, whereas the end portion 28 of the outer tube adjacent to the end of the tube 24 provided with the recess 26 is separated from the outer surface of the tube 24 by an electrically insulating sleeve 29. The inner tube 24 and the outer tube 25 are constructed of metal.

In operation, a mixture of a carrier gas and the gaseous sample flows from the gas chromatography apparatus into the inlet chamber 21 by way of the inlet pipe 23 and the inner tube 24. In order to maintain the sample in the gaseous condition while passing through the pipe 23 and the tube 24, an electric heating current is passed along the pipe 23, the inner tube 24 and the outer tube 25 in order to heat these parts, electrical terminals 30 and 31 being attached to the pipe 23 and the end portion 28 of the tube 24, respectively. The gaseous sample condenses on the inner surfaces of the inlet chamber 21. If all or a part of the carrier gas does not condense, the gas can escape from the interior of the inlet chamber 21 by way of an orifice 32 in the outer tube 25, the space 33 between the inner tube 24 and the outer tube 25, and an outlet opening 34 in the end portion 28 of the tube 25. A sleeve 35 is placed around the tube 25 at a position between the orifice 32 and the outlet opening 34, and the sleeve is fitted inside the end portion of the inlet chamber 21 so that no gas can escape from the inlet chamber except through the orifice 32. A tube 36 containing a desiccant is attached to the outlet opening 34 to prevent the entry of water vapour into the inlet chamber 21.

When the sample has condensed, the inlet nozzle assembly 22 is removed, the open end of the inlet chamber 21 is closed by means of a well-fitting bung, the sampling cell is removed from the bath of refrigerant, and the sample is transferred to the cell chamber by centrifuging. A closure member of the form shown in FIG. 5 is then pressed into the inlet conduit of the sampling cell in order to prevent loss of the sample by vapourisation.

In place of a sampling cell provided with an'integral inlet chamber, a sampling cell provided with an inlet chamber that is non-integral with and separable from the remainder of the sampling cell may be placed in the bath of refrigerant. The sampling cell may be as hereinings. A non-integral inlet chamber alone may be placed in' the refrigerant, provided that the outlet conduit of the inlet chamber is provided with a suitable closure. After the sample has condensed in the inlet chamber, the sample is transferred to a sampling cell by, in the case of a sampling cell of the form shown in FIGS. 2 and 3 of the drawings, centrifuging.

The use of a non-integral inlet chamber has the advantages that only the cell chamber and the inlet conduit of the sampling cell need be placed in the spectrophotometer, and also that the inlet chamber can be cleaned and reused to fill several cell chambers.

I claim:

1. A spectrophotometric sampling cell formed from a tube of material suitable for spectrometric purposes, wherein a portion of the tube forms an inlet conduit and an adjacent portion of the tube is flattened to form a cell chamber that is in communication with the inlet conduit, the cell chamber having two substantially parallel plane walls and the opposing portions of the flattened tube being fused together beyond the lateral edges of the cell chamber.

2. A sampling cell as claimed in claim 1, wherein there is provided a second conduit communicating'with the cell chamber and situated at the end of the cell chamber remote from the inlet conduit, the second conduit being formed from a further portion of the tube.

3. A sampling cell as claimed in claim 1, wherein the sampling cell is provided with an inlet conduit only and the opposing end portions of the flattened tube remote from the inlet conduit are fused together in order to close the end of the cell chamber.

4. A sampling cell as claimed in claim 1, wherein there is provided an inlet chamber having an internal cross sectional area greater than the internal cross-sectional area of the inlet conduit and communicating with the end of the inlet conduit remote from the cell chamber.

5. A sampling cell as claimed in claim 4, wherein the inlet chamber is formed from a further portion of the tube from which the sampling cell is formed.

6. A sampling cell as claimed in claim 1, wherein the cross-section of the inlet conduit of the sampling cell is circular.

7. A sampling cell as claimed in claim 6, wherein the walls of the inlet conduit taper towards the cell chamber.

8. A sampling cell as claimed in claim 1, wherein said material is suitable for use in the infra-red region of the spectrum.

9. A sampling cell as claimed in claim 8, wherein said material is selected from the group consisting of silver chloride and polyethylene.

10. A sampling cell as claimed in claim 1, wherein the thickness of the cell chamber is within the range of from 10 microns to 1 mm.

11. A sampling cell as claimed in claim 1, mounted in a rigid container provided with windows such that radiation can pass through the cell chamber. I

12. A sampling cell as claimed in claim 11, wherein the rigid container is constructed of a rigid inert plastic material.

13. A spectrometric sampling cell formed from a tube of material a portion of which forms an inlet conduit and an adjacent portion thereof is flattened to form a cell chamber in communication with the inlet conduit and having two substantially parallel plane walls and opposing portions which are fused together beyond the lateral edges of the cell chamber and the end edge thereof remote from the inlet conduit, and inlet chamber in the form of a generally tubular vessel, one end portion of the vessel being in the form of an outlet conduit capable of being inserted into the open end of the inlet conduit of the sampling cell, and means for introducing the gaseous sample comprising an inlet nozzle assembly including inlet and outlet pipes in sealed relation with said cell,

References Cited UNITED STATES PATENTS Davidson 6242 Hippie 6242 Majkrzak et a1. 264320 8 3/1960 Jones et a1. 25043.5

5/1962 Jones et a1. 25043.5 5/1954 Bedford.

FOREIGN PATENTS 2/1964 France.

NORMAN YUDKOFF, Primary Examiner US. Cl. X.R.

Levy 264-320 62-42; 264-320 

